Technical Abstract:
Nep1 is a 24 kDa protein produced by Fusarium oxysporum f. sp. erythroxyli in liquid culture. Previous research demonstrated that foliar application of Nep1 causes ethylene production and necrosis of dicot leaves. Pseudomonas syringae pv. tagetis (Pst) has been investigated as a biocontrol agent for Canada thistle. Foliar inundative applications of Pst with an organosilicone surfactant cause apical chlorosis of Canada thistle. However, the efficacy of Pst as a biocontrol agent for Canada thistle is variable, and one or two applications of the bacterium usually do not provide adequate weed control. Growth chamber experiments were conducted to determine whether adding Nep1 to the spray formulation would increase the efficacy of Pst on Canada thistle and two other weeds in the Asteraceae family (common ragweed and dandelion). Foliar treatments were made at 28, 26, and 21 d after planting for Canada thistle, dandelion, and common ragweed, respectively. Efficacy was evaluated by measuring shoot dry wt 2 wk after treatment. The treatments included: (1) untreated control, (2) Silwet L-77(0.3%,v/v) control, (3) Nep1 (5 µg/ml) plus 0.3% Silwet L-77, (4) Pst (10**9 cfu/ml) plus 0.3% Silwet L-77, and (5) Pst (10**9 cfu/ml) and Nep1 (5 µg/ml) plus 0.3% Silwet L-77. For all three weeds, the Silwet L-77 treatment did not have a significant effect on shoot dry wt. Compared to the Silwet L-77 control(treatment 2), treatments 3, 4, and 5 reduced shoot dry wt of Canada thistle by 32, 17, and 40%, respectively. For common ragweed, treatments 3, 4, and 5 reduced shoot dry wt by 24, 66, and 78%, respectively, compared to the Silwet L-77 control. For dandelion, treatments 3, 4, and 5 reduced shoot dry wt by 32, 44, and 68%, respectively, compared to the Silwet L-77 control.